Holographic recording or reconstruction using a beam of coherent light such as that from a He--Ne laser is capable of recording and reproducing a large quantity of information, and holograms can be used as a grating to diffract light. To achieve these results, many optical devices that can record or reconstruct holograms are being developed.
Particularly, intensive efforts are being made to develop holographic devices that can be packed in optical ICs which are small, light and have a high recording density. Typical of the types under development are ones that use a thin As, Se or Te base amorphous film and ones that use a LiNbO.sub.3 waveguide layer having Ti diffused therein. However, the former type is based on a change in phase between the amorphous state and the crystalline state, and is not satisfactory with respect to fidelity and long-term stability. The LiNbO.sub.3 layer used in the latter type has very low photosensitivity. Therefore, neither type of holographic device has been put to commercial use.